High temperature materials have been used extensively in advanced heat engines and energy conversion systems as well as in many industrial engineering systems. High-temperature alloys are needed to improve thermal efficiency through increased operating temperature of heat engines and energy conversion devices. The operative temperature of advanced energy conversion systems is currently limited by structural materials which lose their strength and/or oxidation resistance at high temperatures. Ni-based superalloys can be used at temperatures up to 950° C. in polycrystalline forms and at temperatures approaching 1100° C. in single crystalline forms. Structural ceramics, on the other hand, possess adequate strength at higher temperatures, but their poor fracture toughness and environmental sensitivity greatly restrict their use as engineering materials. There is therefore a need for metallic alloys that can be used as structural materials at temperatures above 1200° C. in oxidizing environments.
For example, nozzle materials for hypersonic wind tunnel use are required to withstand exposure to high-pressure oxidizing gases at temperatures up to 1500° C. Because of the high-temperature requirement, only ceramic materials and refractory metal alloys have been considered for such applications. Ceramic materials have good strength at high temperatures but poor fracture toughness and limited thermal shock resistance at ambient temperatures. Refractory metal alloys, such as Nb and Ta-based alloys, on the other hand, have high melting points and good toughness, but poor oxidation resistance at elevated temperatures. Refractory noble-metal alloys based on Ir are of interest for high temperature use because of their high melting point (˜2440° C.) and good oxidation resistance in air. However, currently existing Ir-based alloys are limited by reduced strength at temperatures above 1200° C. There is a need for Ir-based alloys that retain strength at temperatures above 1200° C.